Radar level gauge (RLG) systems are in wide use for determining filling levels in tanks. An electromagnetic transmit signal is generated by a transceiver and propagated towards the surface of the product in the tank, and an electromagnetic reflection signal resulting from reflection of the transmit signal at the surface is received by the transceiver.
Based on the transmit signal and the reflection signal, the distance to the surface of the product can be determined.
Most radar level gauge systems on the market today are either so-called pulsed radar level gauge systems that determine the distance to the surface of the product in the tank based on the difference in time between transmission of a pulse and reception of its reflection at the surface of the product, or systems that determine the distance to the surface based on the frequency difference between a transmitted frequency-modulated signal and its reflection at the surface. The latter type of system is generally referred to as being of the FMCW (Frequency Modulated Continuous Wave) type.
Radar level gauging is generally performed either by means of non-contact measurement, whereby electromagnetic signals are radiated towards the product in the tank, or by means of contact measurement, often referred to as guided wave radar (GWR), whereby electromagnetic signals are guided towards and into the product by a probe acting as a waveguide. The probe is generally arranged to extend vertically from the top towards the bottom of the tank.
For guided wave radar level gauge systems, different kinds of probes may be used, for example depending on the characteristics of the product in the tank, or the environment in the tank.
For example, in tanks where the probe is arranged close to a wall of the tank and/or disturbing objects in the tank, it may be desirable to use a two-conductor probe in which the radial extension of the electrical field is relatively small, such as a coaxial probe with a signal conductor and a shielding conductor. In such a probe, there is generally an empty space between the signal conductor and the shielding conductor, and spacers are provided for maintaining a stable positional relationship between the signal conductor and the shielding conductor. Moreover, the shielding conductor is generally provided with holes to allow product to enter and exit the space between the signal conductor and the shielding conductor.
Although being advantageous for various applications, a coaxial probe is generally not particularly suitable for some products, such as viscous liquids which may not freely flow through the holes in the shielding conductor, or sticky liquids which may cause clogging and/or fill up the space between the signal conductor and the shielding conductor.
Furthermore, it may be cumbersome or at least time-consuming to arrange spacers for maintaining the positional relationship between the signal conductor and the shielding conductor.
It would thus be desirable to provide a guided wave radar level gauge system with an improved two-conductor probe, in particular a two-conductor probe allowing use with a broader range of products and/or facilitating the arrangement of spacers.